Leads serve to connect semiconductor components to the outside world. They protrude from the semiconductor housing and are bent to a J shape, so that they extend essentially underneath the housing of the semiconductor component. The semiconductor component is mounted on a printed circuit board by placing the leads on pads of the circuit board and soldering them to the pads.
The J-leads are formed by stamping processes. In such processes, faults may occur, particularly due to foreign matter in the die. Since, after the component has been soldered on, such faults can no longer be corrected, because the leads are underneath the component, the leads, particularly their position data, need to be checked directly after the stamping processes. It is particularly important to check the position data in a plane parallel to the bottom side of the housing (xy-plane) for colinearity. Undesired displacements of the leads in the xy-plane may be caused by deformations of the leads. A displacement of the leads in the xy-plane may also be present if the leads are coplanar, i.e., if their respective lowest points are spaced the same distance from the bottom side of the housing. This deformation is also called "bow-in" or "bow-out". Therefore, it is necessary to check position data of the leads in the xy-plane, i.e., for colinearity, independently of a check for coplanarity. Conventional automatic methods, such as transmitted-light measurement techniques, are unsuitable, since the Y-leads disappear for the most part under the opaque component. In practice, therefore, a manual visual inspection is carried out. To do this, several components are arranged along a straight line, for example. The observer looks at each component to see whether the individual leads are spaced approximately the same distance from the straight line. Those components which, in his or her view, have leads with excessive deviations in the xy-plane are then discarded. The reliability of the selection is thus dependent on the observer's watchfulness. Accordingly, a method for automatically checking position data of J-leads at a semiconductor component is highly desirable.